[Universal Steam Metadata] Cancelling still tries to fill out Platform

[chocolatechipcats]

Describe the bug
Possibly related to changes made in #5. When searching a game, then pressing the 'cancel' button, Steam Store still tries to import 'PC (Windows),' increasing the chance that it'll be accidentally overwritten.

To Reproduce

1. Have a game set to 'PC (MS-DOS)' (or any platform other than Windows).
2. Begin a search with metadata provider 'Steam Store.' Cancel it without selecting a game.
3. The game will try to import PC (Windows) anyways.

Screenshots

Diagnostics ID
a7a3dab6-e4b0-434d-b5fa-ddccf5b1b977

[JosefNemec]

I think this was done intentionally in case users changes their mind later, so they can pick that filed from field list on edit game page. This applies to all fields and they shouldn't be actually added to the library in the end, unless you choose to assign them to a game.

[chocolatechipcats]

As the game didn't even exist on Steam in the first place (I think I clicked it by mistake), it was a little unexpected to have it try to import the platform when I'd cancelled at the the search dialog.